Make precise cropping selections using guides

The ability to select part of an image and then modify the selection in one way or another is basic to most everything you do in Photoshop. You can use selections to create masks, define fill-ins, and adjust image values, as shown in Figure A. Sometimes, as you begin honing in on a work in progress, selections need only be general. But at other times, as you finish editing, you must make precise image selections.